Process for surface treatment of metal expansion alloys



3.53am? C6 Patented Sept. 22, 1970 3,530,017 PROCESS FOR SURFACE TREATMENT OF METAL EXPANSICN ALLQYS Floyd Louis Michelson, Chicago, Wilbert Joseph Roberts, Oak Lawn, and Michael Joseph Laney, Chicago, Ill., assiguors to The Diversey Corporation, Chicago, Ill., a corporation of lllinois No Drawing. Filed May 8, 1967, Ser. No. 636,656 Int. Cl. C23f 3/04 US. Cl. l5620 16 Claims ABSTRACT OF THE DISCLOSURE Disclosed is a process for treating low-expansion metals, advisably containing one or more of nickel, iron and cobalt, to improve the surface by controlled metal removal with inhibition of necking and undercutting, while providing a surface having low outgassing characteristics. Brightening of the metal surface can also be obtained if desired. Principally used in the metal treatment process is an acid bath containing nitric and hydrochloric acids and an additive containing a polyethoxyethylene chain. This process also uses additional treatments before and after the acid bath to further improve the metal surface.

Many articles used in the electrical industry require metal-to-glass, metal-toceramic and bimetallic seals, joints and junctures. Transistors, headers, electric tubes, optical equipment, X-ray equipment, radio and television receivers and computers are some articles that require elements using such seals and junctures. Various special metals, generally called low-expansion alloys, are used for such purposes because they have low-expansion properties compatible with those of the materials to which they are joined or connected thus making strong leakproof junctures possible.

Representative low-expansion metals can be essentially all nickel with small amounts of other ingredients but usually are alloys composed of nickel and iron; iron and cobalt; and generally nickel, iron and cobalt with and without small amounts of other minor constituents. Thus a group of the presently useful low-expansion alloys can have the following composition:

Percent by weight Nickel -100 Iron 0-80 Cobalt 0-25 Minor constituents 0-5 Although chromium can be present, it usually is excluded, but, in any event, is generally not present in an amount above Some of the minor constituents which can be present are chromium, aluminum, sulfur, phosphorous, carbon, silicon, manganese, zirconium and titanium.

During fabrication of articles made from such lowexpansion metal alloys, they are often welded, brazed, soldered, machined and/or subjected to some other heat treatment which produces a heat scale. This heat scale is unsightly and can tend to aggravate corrosion of the article and interfere with subsequent operations, such as electroplating as with gold. Consequently, it is generally removed by either heat treatment in a reducing atmosphere or chemical means. In addition to removal of heat scale, metal alloys are often subjected to chemical operations to improve their appearance and corrosion resistance.

Conventional chemical baths have a tendency to remove unduly large quantities of metal from the article and thus adversely affect dimensional accuracy of the article, which is a matter of great importance, such as with wire that is often not more than mils thick and foil which is often not more than 10 mils thick.

It is one of the purposes of the present invention to overcome this disadvantage and to provide chemical methods and compositions that produce a microfinished surface on low-expansion alloys with controlled, reproducible metal removal to produce very small dimensional changes. A microfinished surface is one which under magnification shows an extremely level continuous surface with refined grain boundaries.

A further advantage of this invention is that it significantly reduces necking and undercutting during finishing of low-expansion alloy metal-to-glass, and metal-toceramic, junctures and seals of transistors, headers, optical equipment, X-ray equipment, electronic equipment and the like. Necking is defined as a greater rate of preferential attack by the bath near junctures of metal alloy leads and headers with ceramic or glass seals used in transistors and other components, and also at bimetallic junctions, resulting in a greater dimensional change, as shown by smaller diameters, than in other areas of the part being treated. Such necking has been found to be caused by prior chemical polishing compositions.

A further advantage of this invention is that it reduces or prevents rounded contours on sharp or square components made from low-expansion alloys such as posts, connectors, leads, or lips of transistors, headers, optical equipment and X-ray equipment and the like.

A further advantage of this invention is that it significantly increases the bonding of silicon and germanium to the primary (base) or secondary (plated) surface of transistors, headers, optical equipment, X-ray equipment, electronic equipment and the like.

A further advantage of this invention is that it significantly reduces intergranular corrosion of such processed low-expansion alloy metal parts.

A further advantage of the invention is that it levels the surface, decreasing the difference between the true and apparent surface area of low'expansion alloy components. The apparent surface area is simply the superficial area obtained by measuring length and width. However, the true surface area is generally much larger due to surface roughness.

A further advantage of this invention is that it can be used in connection with electroor mechanical polishing as a pretreatment thereby saving valuable time, materials, and labor by reducing the amount of mechanical or electro-polishing required.

According to one aspect of the present invention, it has been discovered that low-expansion alloys such as described previously, can be readily treated and desmutted by contacting the alloy sequentially with three treating solutions which for convenience shall be labeled:

(1) Microfinishing solution.

(2) Desmutting with alkaline permanganate solution.

(3) Alkaline film removal with acid solution.

The invention, however, is also particularly concerned with the single microfinishing step since it gives results not previously obtainable using prior solutions. Furthermore, it is sometimes advantageous to precondition the alloy surface with oxide removing solutions prior to heat treatment and prior to use of the microfinishing solution and the details for such prior treatment will also be given hereinafter.

Although the invention is useful for treating low-expansion alloys as described hereinabove, it is particularly useful for surface treatment of low-expansion alloys of the compositions:

Percent by weight Nickel 20-50 Iron 25-70 Cobalt 1025 Minor constituents 0-2 plus, if desired, small amounts of minor ingredients such as manganese, silicon and carbon. More specifically, this invention is useful for surface treatment of:

(a) Low-expansion alloys containing no cobalt and commercially known as Invar which contain 30-36% Ni, 70-64% Fe plus minor alloying constituents, or similar alloys containing 30-60% Ni per composition and the balance 40 to 70% is iron.

(b) Low-expansion alloys containing no cobalt typically known commercially as Ferrovac 42 Ni which contains 42.0% Ni, 0.08% C, 0.40 to 1.0% Mn, 0.25% Si and the remainder Fe.

(c) Glass-to-metal sealing low-expansion alloys containing cobalt and commercially known as Kovar, Rodar and Nicoseal which typically contain 29.0% Ni, 17.0% Co, 0.45% Mn, 0.10% Si, 0.02% C, and the remainder Fe.

((1) High nickel alloys including those which are substantially 100% nickel.

A specific commercially available, and widely used, low-expansion alloy which can be treated according to this invention is sold under the trademark Kovar and has the following composition:

Percent by weight Nickel 29 Cobalt 17 Manganese 0.45 Silicon 0.10

Carbon 0.02 Iron Remainder Another specific low-expansion alloy which is commercially available, and which can be treated according to this invention, is Invar having the composition:

Percent by weight Iron 63.8 Nickel 36.0 Carbon 0.2

A high nickel low-expansion alloy which can be treated according to this invention is Grade 200 nickel having about the following composition:

Percent by weight Nickel 99.435

Carb on 0.06 Manganese 0.25 Iron 0. l Sulfur 0.005 Silicon 0.05 Copper 0.05

(1) THE MICROFINISHING TREATMENT In this step, the low-expansion alloy surface is microfinished by contacting it with an aqueous solution containing hydrochloric acid and nitric acid, with or without phosphoric acid, and an additive having a polyoxyethylene chain in its molecule. In the absence of the additive, the aqueous acid mixture produces a nonuniformly etched, rough surface. The additive modifies the chemical action of the solution so that it reacts to produce a smooth finish with minimum dissolution of base metal.

The bath for the microfinishing step is advisably an aqueous solution containing about 1% to 20% by weight of hydrochloric acid, about 1% to 8% by weight of nitric acid, about 0.1% to about 20% and advisably about 0.2% to of an additive selected from the grOup consisting of: (1) condensation products of one mole of phenol with about 5-30 moles of ethylene oxide; (2) condensation products of 1 mole of an alkyl phenol having up to about 15, and preferably up to about 12, carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide; (3) condensation products of one mole of an alkyl amine having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide; (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide; (5) condensation products of 1 mole of a polypropylene glycol containing about 1050 propylene oxide units with about 4-150 moles of ethylene oxide; (6) polyethoxylated quaternary ammonium salts having 2-50 moles of ethylene oxide combined with each mole of quaternary amine; and (7) mixtures thereof. It can be seen that the additives are characterized by the presence of at least one polyoxyethylene chain within the molecule, i.e., a chain composed of recurring groups. The number of moles of ethylene oxide which are condensed with one mole of parent compound (i.e., alkyl phenol, alkyl amine, aliphatic amine, or aliphatic alcohol), depends on the molecular weight of the hydrophobic portion of the condensation product. The additives of the invention should contain suflicient ethylene oxide units to insure the solubility thereof in the acid bath. In general, compounds which are soluble in the acid bath can be formed by condensing the reactants in the proportions given above.

In addition to phenol, alkyl phenols are condensed with ethylene oxide to form one of the additives used in the invention. Alkyl phenols which can be used include those in which the alkyl group contains 1 to about 15, and preferably 1 to about 12, carbon atoms in a straight or branched chain, which can be saturated or unsaturated. Particularly preferred additives comprise the condensation products of one mole of isooctylphenol or nonylphenol, condensed with about 10 moles of ethylene oxide. Examples of other suitable alkylphenol ethylene oxide condensation products are those in which the hydrophobic portion of the product is derived from phenol, methylphenol (cresol), ethylphenol, hexylphenol, decylphenol, dodecylphenol and the like.

Among the other ethylene oxide condensation products which are used in the invention are those wherein an alkyl amine or aliphatic alcohol, in which the alkyl group in each case has about 10 to about 20 carbon atoms in a straight or branched chain, which can be saturated or unsaturated, is condensed with about 5-50 moles of ethylene oxide. Examples of suitable compounds are the condensation products of ethylene oxide with decylamine, dodecylamine, tridecylamine, hexadecylamine, octadecylamine, and the like; and with decyl alcohol, dodecyl alcohol, tridecyl alcohol, hexadecyl alcohol, octadecyl alcohol and the like.

A further class of ethylene oxide condensation products which can he used in the invention is that in which a polypropylene glycol is used as the parent compound. The polypropylene glycol should normally be water-insoluble, i.e., it should be composed of more than about 10 propylene oxide units, suitably about 10-50 propylene oxide units. For use in the invention, such a polypropylene glycol is condensed with sutficient ethylene oxide to insure the solubility of the product in the microfinishing bath, e.g., about 4-160 moles of ethylene oxide per mole of glycol.

A further class of ethylene oxide condensation products which can be used in the invention is the polyethoxylated quaternary ammonium salts having the following general chemical structure:

(IJIIS [RN-(CH2C Hzohll] Z- (t ilrzonzomr where Z is an anion such as chloride or sulfate, R represents a hydrocarbon group having advisably 12-18 carbons such as a saturated or unsaturated alkyl chain derived from either oleic, stearic or coco fatty acids. The polyoxyethylene content, indicated by x and y, is dependent on the particular polyethoxylated aliphatic amine quaternized. The polyethoxylated aliphatic amines of this invention have 2-50 moles of ethylene oxide combined with each mole of fatty amine. A typical polyethoxylated quaternary ammonium salt of this invention is described as a cationic quaternary polyethoxylated stearic amine surfactant of the following general structure:

The above is one mole of N-methyl octyldecylamine reacted with 15 moles of ethylene oxide and quaternized with methyl chloride (CH Cl).

Superior chemical microfinishing is obtained with a bath containing about 2% to 20% by weight of hydrochloric acid, about 2% to- 8% by weight of nitric acid, about 0.2% to 15% by weight of the additive and the remainder water. A preferred specific embodiment of the microfinishing bath of the invention comprises 3% by weight of hydrochloric acid, 3% by weight of nitric acid, 1% by weight of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide, and the remainder Water. Optionally, there may be included in this preferred embodiment about 20% by weight of phosphoric acid.

The action of the microfinishing bath of the invention is enhanced by the addition thereto of phosphoric acid. Phosphoric acid appears to inhibit pitting and to stabilize the microfinishing bath. The phosphoric acid can be used in a concentration up to 60% by Weight of the total bath, and preferably is used in amounts from and 35% by weight of the bath.

In all the above solutions, the concentrations of acids are expressed as percents by weight, on an anhydrous basis, of the total bath with the acids being considered of 100% strength. Unless otherwise stated, the percents hereinafter given, including the claims, for the acids is on this basis.

The low-expansion alloy metal to be treated is suspended in the hot microfinishing bath at a temperature of about 130-200 F., and preferably within the range from about 160l90 F. The time required to produce a suitable surface will vary somewhat depending on the composition and temperature of the bath, the type of metal surface to be rnicrofinished, and the condition of the surface. For normal microfinishing, the time required is ordinarily about 3 to 15 minutes.

The action of dilute baths on the low-expansion alloy is not very susceptible to time and temperature variations, nor does a small change in bath composition affect the quality of finish obtained, as for example the slight dilution of the bath resulting when metals previously treated in some other bath, and retaining a quantity of moisture on their surfaces, are immersed in the microfinishing bath. Furthermore, a dilute bath is considerably less expensive than a concentrated bath.

No unusual or specially constructed equipment is required for the microfinishing process. Readily available acid resistant containers and heating elements are the only materials required.

The microfinishing baths of this invention achieve the desired rnicrofinished surface without producing significant necking or undercutting at junctures of the alloy to glass or ceramic materials. Previously used baths very drastically undercut such junctures and caused severe necking at the junctures of alloy wires to glass and ceramic materials. The Wires, usually 25 mils thick or less, so necked were weak and broke readily upon bending. Undercut junctures led to leaks, preventing obtaining or maintenance of the needed vacuum in electronic tubes and equipment. The microfinishing step of this invention eliminates these problems While giving a very bright alloy surface.

The microfinishing solutions are also especially useful in treating low-expansion alloy foil, especially such foil of 10 mils thickness or less of the type used in fabricating circuitry of minute size for electronic purposes. Such foil, in addition to being very thin, often has many cutout areas With numerous edges and pin-size leads for joining into circuits. It is essential in treating such foil that the desired effect he obtained with readily controlled removal of metal for otherwise the foil will be rendered unfit for use. The microfinishing solutions provided herewith permit controlled surface finishing over a wide range of use conditions. Thus, the microfinishing solutions can be used on low-expansion alloy foil, and even Kovar 4 mils thick, with representative immersion times from 3 to 10 minutes at representative bath temperatures of F. with removal of only about 0.5-0.8 mils of metal. Previously used baths had to be used at room temperature because even at such temperature they removed 1l.5 mils of metal in 3-5 seconds, thus preventing controlled metal removal on a micro scale.

In addition to using relatively low-cost ingredients, the working solutions are used at low concentrations, thereby minimizing drag-out losses. In addition, no hydrofluoric acid is used, an ingredient which is commonly used in metal descaling solutions, and which is quite toxic and corrosive to skin. Moreover, because of the relatively small removal of base metal occasioned by the process of the invention, variations in the size of the finished object are kept to a minimum.

For handling and storage purposes, the microfinishing bath of the invention may be supplied in a concentrated mixture to which is added nitric acid and water to make the Working solution. Concentrates of this type may suitably contain about 6% to 30% by Weight of hydrochloric acid, about 2% to 20% by weight of the additive, optionally about 25 %to 65% by weight of phosphoric acid, and the remainder water. A particularly preferred example of such a concentrate contains about 8% by weight of hydrochloric acid, about 60% by Weight of phosphoric acid, about 2.6% by weight of the condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide and the remainder water.

(2) DESMUTTING BY ALKALINE PERMAN- GANATE TREATMENT Following the microfinishing step, the low-expansion alloy is advisably treated with an alkaline permanganate solution to remove smut. The desmutting can be effected by contacting the alloy surface with an aqueous alkaline oxidizing solution at an elevated temperature. Of course, if the presence of smut is not a problem, steps 2 and 3 of the process need not be pursued.

More particularly, the desmutting can be effected with an aqueous caustic solution containing an alkali metal permanganate. The solution advisably contains about 2% to 8% by weight of potassium or sodium permanganate and about 5% to 20% by Weight of an alkali metal hydroxide, such as sodium or potassium hydroxide. A water softener also may be included, such as an alkali metal carbonate, preferably sodium or potassium carbonate. The softener is employed in a minor effective amount, is being preferred to employ a carbonate in a proportion of about 0.5% to 1% by weight of the solution. A particularly useful solution can have the composition:

Grams per liter of solution Sodium hydroxide 80 Potassium permanganate 40 Sodium carbonate 10 Water Balance The desmutting solutions as described can be employed suitably at a temperature of about 180-210 F. for about l-5 minutes after which the alloy can be rinsed with cold water.

The desmutting treatment leaves an alkaline film on the surface of the low-expansion alloy surface, particularly on the surface of Kovar parts, and it is accordingly removed by the next step.

(3) ALKALINE FILM REMOVAL WITH ACID SOLUTION The alkaline film left on the expansion alloy surface following the desmutting step is conveniently removed by contacting the alloy surface with an acid. A wide variety of strong acids can be used for this purpose including 220% aqueous hydrochloric acid, 2%-l00% aqueous sulfuric acid, %-85% phosphoric acid, 1%-10% aqueous nitric acid and 2%-100% aqueous acetic acid. The microfinishing bath can also be used for this purpose since it is acidic. The concentration of acid should be sufificient to remove the film but not significantly etch the alloy surface.

The alkaline film is generally removed in about seconds to 2 minutes using the acid solution at ambient temperature. Specifically, a 10% hydrochloric acid solution at room temperature removes the film in about seconds.

Following the acid treatment, the alloy surface is rinsed with cold water and dried.

The described microfinishing procedures achieve the desired smooth surface while simultaneously inhibiting necking and undercutting at the juncture of low-expansion alloy-to-glass or ceramic seals. Necking and undercutting result with the use of prior baths, but not with our microfinishing bath, even though both ours and the prior art baths generally brighten the metal to some extent. In addition, a controlled metal loss, such as about 0.1-0.3 mil in one minute immersion in the microfinishing bath is achieved, Which is far less than the metal loss with conventional baths. This is very important because of the thinness of the low-expansion alloy wires and foils used in the electronic industry where loss of metal can render parts unacceptable for use. Furthermore, lowexpansion alloys when treated as described, produce loW- outgassing under high vacuums such as 10 torr, even when joined to glass or ceramic material.

The described procedures are suitable for micro-finishing low-expansion alloys whether or not they have been subjected to a prior heat treatment. However, it has been found advisable for best surface preparation of alloy parts which are heat treated as a part of fabrication procedures before microfinishing, such as in the formation of alloy-to-glass or ceramic seals or junctures, to condition the surface of the alloy by contacting it with a phosphoric acid solution before it is heat treated, Furthermore, even better results are obtained by treating the alloy surface With a weakly alkaline solution, after treatment with the phosphoric acid solution and before heat treatment. The prior conditioning leads to ready deoxidizing of heat treated surfaces by use of the described procedures and to a very fine grain structure on the surface of the microfinished alloy.

In the preconditioning treatment, an aqueous solution is advisably used containing about 4% to 50% by weight of phosphoric acid and also advisably, but optionally, from about 0.25% to 30.0% by Weight of a surfactant such as the additives, which are surfactants, herein described previously with regard to the microfinishing bath operation, as well as other surfactants.

Other surfactants which can be employed include those containing an aliphatic chain of 6 to 20 carbon atoms. A preferred group of surfactants includes the cationic aliphatic, araliphatic and heterocyclic amines, nonionic and anionic aliphatic acid amides, nonionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aliphatic aryl polyether sulfonates, and anionic aliphatic phosphates.

The cationic aliphatic, araliphatic and heterocyclic amines are primary, secondary, tertiary and quaternary amines containing at least one aliphatic chain of 6 to 20 carbon atoms, which may be a straight or branched chain. Representative compounds include the mono-, diand trin-alkyl fatty amines. Exemplary compounds include the primary, secondary and tertiary fatty amines identified by the trade name Armeen. Armeen-8 is a monoalkyl amine having 6-8 carbons in the alkyl group. I

Other compounds include the alkyl and the aralkyl quaternary ammonium salts. Preferred compounds of this type contain one alkyl group having from 8 to 16 carbon atoms, two alkyl groups having from 1 to 6 carbon atoms, and an aralkyl group having from 7 to 10 carbon atoms, such as alkyl dimethyl ethylbenzyl ammonium chloride identified by the trade name Onyx BTC 471.

The heterocyclic amines include the substituted glyoxalidines and the substituted oxazolines, employed as their acid addition salts. Representative compounds include l-hydroxyethyl 2 heptadecenyl glyoxalidine identified by the trade name Alro Amine O, and 2-heptadecyl- S-methyl-S-hydroxymethyl oxazoline identified by the trade name Alkaterge C.

The non-ionic aliphatic acid amides include the amides of preferably lower aliphatic amines such as aminoethyl ethanolamine and diethanolamine and fatty acids having a straight or branched aliphatic chain of 6 to 20 carbon atoms. Representative compounds include aminoethyl ethanolamine fatty acid amides identified by the trade name Nopcogen RP and diethanolamine capryl amide.

The anionic aliphatic acid amides include the amides of 6-20 carbon atom straight or branched chain aliphatic acids with preferably loWer aliphatic aminosulfonic and aminocarboxylic acids. The amino group preferably is also substituted With a 1-6 carbon atom alkyl group. Representative compounds include sodium N-cyclohexyl N-palmitoyl-taurate identified by the trade name Igepon CN-42, sodium N-methyl-N-oleoyl-taurate identified by the trade name Igepon T-33, and N-methyl-N-oleoyl-glycine identified by the trade name Sarkosyl O.

The nonionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers include the 6- 20 carbon atoms straight or branched chain aliphatic acid partial esters of sorbitol, propylene glycol, and glycerol, and their polyoxyethylene ethers. Representative compounds are sorbitan monooleate identified by the trade name Span and polyoxyethylene sorbitan monooleate, called Tween 80.

The anionic aliphatic sulfates include the 6-20 carbon atom straight or branched chain alkyl sulfates or sulfate esters. A representative compound is sodium lauryl sulfate identified by the trade name Duponol C.

The anionic aliphatic esters and amides of sulfonated dicarboxylic acids include the 6-20 carbon atom straight or branched alkyl esters of sulfonated lower dicarboxylic acids. A representative compound is sodium sulfosuccinic acid dioctyl ester identified by the trade name Aerosol OT and disodium N-octadecylsulfosuccinamate identified by the trade name Aerosol 18.

The anionic aliphatic aryl polyether sulfonates include the 6-20 carbon atom straight or branched chain alkyl substituted aryl polyether sulfonates. A representative compound is sodium octyl phenoxy polyethoxy sulfonate identified by the trade name Triton X-200.

The anionic aliphatic phosphates include the 6-20 carbon atom straight or branched chain alkyl monoand poly-phosphates containing up to 8 phosphate radicals. Representative compounds include 2-ethylhexyl) Na (P 0 Z identified by the trade name Victawet 35B and (capryl) Na (P D identified by the trade name Victawet 58B and monophosphates such as lauryl ester of ortho phosphoric acid.

Additional surfactants which may be employed include the anionic fluorinated aliphatic compounds such as Florochemical FC-95 and the amphoteric surfactants such as the ethoxylated sodium salt Triton QS-15.

Hydrochloric acid and sulfuric acid are avoided because they are generally too strong for suitable preconditioning.

The low-expansion alloy is conveniently contacted with the phosphoric acid solution at a moderately elevated temperature such as 120 F. to 190 F. for about 0.5 to 20 minutes. The alloy surface can then be rinsed with water.

A particularly useful phosphoric acid composition for such conditioning can contain the following ingredients:

Percent by weight Phosphoric acid 25 Xylene sulfonic acid 20 Nonylphenol-ethylene oxide condensate (1:10 mole ratio) 2 Water 53 A 50% by weight solution of this composition at 150 F. for 10-15 minutes is particularly useful for the first step of the preconditioning. The alloy surface can then be rinsed with water.

In the preferred process of preconditioning, the metal surface is next contacted with an aqueous solution of an inorganic complex phosphate, such as an alkali metal, i.e., sodium or potassium, tripolyphosphate, pyrophosphate or hexametaphosphate. The solution advisably contains about 2% to 20% by weight of complex phosphate. It is also highly desirable to include an alkali metal carbonate, and/or bicarbonate, and particularly sodium carbonate and/or bicarbonate, in the solution for buffering and cleaning action. Thus, from about to 40% by Weight of alkali metal carbonate and/ or bicarbonate can be included in the solution. Other optional ingredients such as any of the surfactants described previously can be included, such as in amounts of about from 0.25% to 20% by weight of the solution. Borax can also be included in the solution for additional cleaning power.

The aqueous complex phosphate solution can be used to treat the metal surface at about 120 to 190 F. for a short period such as about 0.5 to 20 minutes. The metal surface can then be rinsed with water.

A specific complex phosphate composition which can be used in the preconditioning is as follows:

Percent by weight Tetrasodium pyrophosphate 45.00 Sodium tripolyphosphate 13.50 Sodium carbonate 12.00 Sodium bicarbonate 25.00 Sodium lignin sulfonate 2.50 Octylphenoxy poly-(ethyleneoxy) ethanol 2.00

This composition, used at about 8 oz./gal., gives a solution which at 170 F. completes the preconditioning in about 5 to minutes. The alloy surface can then be rinsed with cold water and dried.

The following examples of the invention are given for illustration only and it is not intended that the claims be limited to the specific concentrations of these examples.

EXAMPLE 1 Specimens of the low-expansion alloy Kovar, as above described, are vapor degreased using trichloroethylene, treated with a 10% by volume hydrofluoric acid aqueous solution at room temperature for 7 minutes as is done when there is a need to remove residual glass after a Kovar-to-glass joint is made, rinsed with cold water, pickled in a solution made up of 54.3 lbs. of 28% hydrochloric acid and 45.2 lbs. of water at 140 F. for 1 minute and rinsed with cold Water.

The specimens of Kovar are then immersed in a microfinishing bath consisting of 3% by Weight of hydrochloric acid, 3% by weight of nitric acid, and as the. additive, 1% by weight of the condensation product of 1 mole of isooctylphenol with 10 moles of ethylene oxide, 24% of phosphoric acid, and the remainder water, the bath being maintained at a temperature of 190 F. After 5 minutes of immersion, the specimens are Withdrawn, soaked in Water for 2 minutes and then returned to the bath for a further 2 minutes at the end of which time they are removed, washed and rinsed. As a result of this treatment, the panels acquire a microfinish surface but containing smut.

The panels are treated in an aqueous bath consisting of 4% potassium permanganate and 10% sodium hydroxide at 190 F. for 3 minutes. This removes a dark residue, commonly termed smut. Removing the smut significantly improves the plating quality of the part.

The specimens of Kovar are then treated with a bath consisting of 10% hydrochloric acid at 75 F. for 1 minute, rinsed in cold water and dried.

EXAMPLE 2 Example 1 is repeated using a bath (3% hydrochloric acid, 3% nitric acid) containing no additive. The surface of the panels is rough and irregular from this treatment. In addition, there is non-uniform metal removal from the panel surfaces.

EXAMPLE 3 Example 1 is repeated using a microfinishing bath containing 5% hydrochloric acid, 3% nitric acid, and 1% of the same additive. Results equivalent to those of EX- ample 1 are obtained.

EXAMPLE 4 Example 1 is repeated using a microfinishing bath containing 3% hydrochloric acid, 5% nitric acid, and 1% of the same additive in the bath. The results are equivalent to those obtained in Example 1.

EXAMPLE 5 Example 1 is repeated using a microfinishing bath consisting of 3% hydrochloric acid, 3% nitric acid, 15% phosphoric acid and 1% additive in the bath at F. for 20 minutes. Results equivalent to those in Example 1 are obtained.

EXAMPLES 6, 7, & 8

Example 1 is repeated using a microfinishing bath consisting of 3% hydrochloric acid, 3% nitric acid, 24% phosphoric acid and 1% of the additives identified in Table 1. Microfinishing of the panels, with removal of smut is obtained in each case.

TAB LE 1 are subjected to all the treatments of Example 1. The specimens become bright and free of scale.

EXAMPLE 10 An article is prepared consisting of a piece of Kovar low-expansion alloy having attached thereto by means of gold and silver solder, pieces of Kovar, mild steel, copper and brass. The soldering causes the formation of a heavy blue-black heat scale on the Kovar low-expansion alloy. This article is fully treated as in Example 1. As a result of this treatment, the Kovar low-expansion alloy surface is microfinished and becomes clean and bright, the, copper and brass become clean, the mild steel gives evidence of a light attack, and there is practically no attack on the gold or silver solder. There 1 1 is furthermore no evidence of any adverse galvanic action which might be expected from the presence of the dissimilar metals in contact with an electrolyte.

EXAMPLE 1 1 Example 1 is repeated in all respects except that the sodium hydroxide permanganate solution is replaced with a 4% sodium hydroxide bath at 190 F. for 3 minutes. The microfinished parts are still smutty and cannot be satisfactorily plated.

EXAMPLE l2 Specimens of Kovar are preconditioned by being processed in a bath consisting of 20% phosphoric acid, 2% of the condensation product of 1 mole of isooctylphenol with moles of ethylene oxide and 1% of xylene sulfonic acid at 140 F., for 5 minutes, followed by a cold water rinse, and then treated in a bath consisting of sodium bicarbonate, 5% tetrasodium pyrophosphate, 1% sodium tripolyphosphate, 2% doceylbenzene sulfonic acid and 1% of the condensation product of 1 mole of isooctylphenol with 12 moles of ethylene oxide at 160 F. for 1 minute. These parts are then heat treated for fabrication, which produces a light to dark gray surface. The specimens are then treated as in Example 1 following which the parts have a microfinished smooth surface free of smut.

EXAMPLE l3 Specimens of Kovar are not pretreated, as described in Example 12, prior to heat treating for fabrication. After treatment in the microfinishing bath of Example 1, a black residue called smut is produced over the microfinished surface.

EXAMPLE 14 Example 12 is repeated with a Kovar wire-to-glass seal specimen. The wire is about 15 mils thick. This produces a microfinished surface noticeably free of necking and selective attack at the Kovar-glass juncture after the microfinishing step and before desmutting. The elimination of the necking effect significantly increases the mechanical fatigue life of the part.

EXAMPLE 15 Kovar wire-to-glass specimens are treated with a widely used solution consisting of 75% acetic acid and nitric acid at 70 F. for 5 seconds. This produces a bright surface with severe necking or notching at the Kovarglass juncture. This necking causes the Kovar wire to break on bending.

EXAMPLE 16 A specimen of Kovar foil 4 mils thick is processed in a microfinishing bath consisting of 3% hydrochloric acid, 3% nitric acid, 24% phosphoric acid, 1% of a condensate of 1 mole of isooctylphenol with 1 to 10 moles of ethylene oxide and the remainder water, the bath being maintained at a temperature of 170180 F. After 5 minutes immersion, the thin foil shows a reproducible metal loss of 0.5 mil, producing a smooth surfaced component 3.5 mils thick suitable for electroplating. The surface is not mirror bright or specular to the unaided eye.

EXAMPLE 17 A specimen of Kovar foil 4 mils thick is processed in a widely used bath consisting of 75% acetic acid and 25% nitric acid at room temperature for 5 seconds. After 5 seconds of immersion, the foil shows an irregular metal loss of 2-3 mils, producing a bright irregular surface unsuitable for electroplating.

EXAMPLE 18 Specimens having '[nvar-glass seals are processed in a bath consisting of 20% phosphoric acid, 2% nitric acid,

12 3% hydrochloric acid, 2% of a condensation product of 1 mole of isooctylphenol with 10 moles of ethylene oxide, and the remainder water, the bath being maintained at a temperature of 160 F. After 2 minutes of immersion, the specimens are withdrawn, soaked in distilled water for 60 seconds and oven dried. As a result of this treatment, minimum out-gassing at high vacuum is produced and there is no significant undercutting of the metal-glass seal. The components are not bright or specular to the unaided eye.

EXAMPLE 19 Specimens having Invar-glass seals are processed in a widely used solution consisting of 73% acetic acid, 25% nitric acid and 2% hydrochloric acid, the bath being maintained at a temperature between 70130 F. After l0l5 seconds of immersion, the specimens are withdrawn, soaked in distilled water for 60 seconds and oven dried. As a result of this treatment, excessive leaking at high vacuum is produced due to severe undercutting of the Invar-glass seal.

EXAMPLE 20 Specimens of Kovar low-expansion alloy metal wire are treated in five chemical baths to produce a surface with low out-gassing at high vacuum, controlled metal removal, no necking or undercutting at glass junctures, no smut and a microfinished appearance suitable for electroplating. The treatments are as follows:

(1) Treat in a bath consisting of 8% phosphoric acid, /2 isooctylphenol ethylene oxide condensate (1:10 mole ratio) and 3% sodium doceyl diphenyl ether disulfonate for three minutes at 160 F., followed by water rinsing.

(2) Treat in bath consisting of 10% sodium bicarbonate, 2% tetrapotassium pyrophosphate, /2% sodium lauryl sulfate and 4% nonylphenol ethylene oxide condensate (1:12 mole ratio) at F. for 3 minutes, followed by water rinsing.

(3) After heat treatment and fabrication, treat in bath consisting of 4% hydrochloric acid, 5% nitric acid, 30% phosphoric acid, 1% of an isooctylphenol ethylene oxide condensate (1:10 mole ratio) and the remainder water at 173 F. for 7 minutes, followed by water rinsing.

(4) Treat in bath consisting of 10% sodium hydroxide and 6% potassium permanganate at 200 F. for 4 minutes, followed by water rinsing.

(5) Treat in bath consisting of 10% hydrochloric acid at 75 F. for 1 minute and rinse in water.

EMMPLE 21 Example 20 is repeated replacing steps 1 and 2 with a pretreatment bath consisting of 50% hydrochloric acid, 7% ferric chloride, /t% dodecylbenzene sulfonic acid and the remainder water. Kovar specimens treated in this bath at F. for 4 minutes develop intergranular corrosion as viewed under magnification. Smut and unsatisfactory surface preparation result using a bath consisting of 4% hydrochloric acid, 5% nitric acid, 30% phosphoric acid, 1% of an isooctylphenol ethylene oxide condensate of a 1:10 mole ratio, and the remainder water.

EXAMPLE 22 Example 20 is repeated replacing the bath of step 1 with a bath consisting of 35% phosphoric acid and 2% sodium dodecyl diphenyl ether disulfonate at F. for 3 minutes. The final microfinish is the same as obtained in Exemple 20.

EXAMPLE 23 Example 20 is repeated replacing the bath of step 2 with a bath consisting of 1% sodium tripolyphosptate, 2% sodium bicarbonate, 0.1% nonylphenol-ethylene oxide condensate (1:12 mole ratio) and 0.2% sodium dodecylbenzene sulfonate. Specimens processed in the bath produce excellent parts similar to Example 20.

13 EXAMPLE 24 Example 20 is repeated replacing the bath of step 2 with a bath consisting of 10% tetrapotassium pyrophosphate, 10% sodium bicarbonate, 10% sodium carbonate and 3% of a condensation product of 1 mole of propylene glycol containing 10 moles of propylene oxide units with 50-60 moles of ethylene oxide. Specimens processed in this bath produce good smooth parts similar to Example 20.

The foregoing detailed description has been given for clearance of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. The method of microfinishing the surface of a lowexpansion alloy which has the composition:

Percent by weight Nickel 20-50 Iron 25-70 Cobalt 10-25 which comprises contacting said alloy surface with an aqueous solution consisting essentially of about 1% to 20% by weight of hydrocholoric acid, about 1% to 8% by Weight of nitric acid, about 0.1% to 20% by weight of an additive selected from the group consisting of: (1) condensation products of 1 mole of phenol with about -30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about -20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-150 moles of ethylene oxide, (6) polyethoxylated quaternary ammonium salts having 2-50 moles of ethylene oxide combined with each mole of quaternary amine, and (7) mixtures thereof, and the remainder water, to microfinish the alloy surface and, when said alloy is joined to a glass or ceramic material, said method being effected Without significant necking or undercutting at any juncture of the alloy to glass or ceramic material.

2. The method of claim 1 in which, after said described treatment, the alloy surface is contacted with an aqueous caustic solution containing an alkali metal permanganate to remove smut and then the alloy surface is contacted with an acid to remove alkaline film thereon.

3. The method of claim 1 in which the low-expansion alloy is about 29% nickel, 17% cobalt, 0.45% manganese, 0.10% silicon, 0. 02% carbon and the balance is iron.

4. The method of claim 1 in which the microfinishing solution includes about to 35 phosphoric acid.

5. The method of claim 1 in which the additive is a condensation product of 1 mole of isooctylphenol with about 10 moles of ethylene oxide.

6. The method of claim 1 in which the additive is a condensation product of 1 mole of nonylphenol with about 10 moles of ethylene oxide.

7. The method of claim 4 in which the solution contains about 3 to 5% hydrochloric acid and about 3 to 5% nitric acid.

8. The method of microfinishing the surface of a lowexpansion alloy which has about the composition:

Minor constituents Percent by weight Nickel 30-60 Iron 40-70 which comprises contacting the alloy with a solution consisting essentially of about 1% to by weight of hydrochloric acid, about 1% to 21% by weight of nitric acid, about 0.1% to 20% by weight of an additive selected from the group consisting of: (1) condensation products of 1 mole of phenol with about 5-30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-160 moles of ethylene oxide, (6) polyethoxylated quaternary ammonium salts having 2-50 moles of ethylene oxide combined with each mole of quaternary amine, and (7) mixtures thereof, and the remainder water, to remove scale and produce a microfinished surface and, when said alloy is joined to a glass or ceramic material, said method being effected without significant necking or undercutting at any juncture of the alloy to glass or ceramic material.

9. The method of claim 8 in which the alloy is about 30 to 36% nickel and 64 to 70% iron.

10. The method of claim 8 in which the alloy contains about 63.8% iron and 36% nickel.

11. The method of claim 8 in which the microfinishing solution includes about 15 to 35% phosphoric acid.

12. The method of claim 11 in which the solution contains about 3 to 5% hydrochloric acid and about 3 to 5% nitric acid.

13. The method of microfinishing the surface of a lowexpansion alloy foil of not more than 10 mils thickness, said alloy having about the composition:

Percent by weight Nickel 20-50 Iron 25-70 Cobalt 1*0-25 Minor constituents 0-2 or said alloy having about the composition:

Percent by weight Nickel 30-60 Iron 40-70 which comprises contacting said foil surface with an aqueous solution consisting essentially of about 1% to 20% by weight of hydrochloric acid, about 1% to 8% by weight of nitric acid, about 0.1% to 20% by weight of an additive selected from the group consisting of: (1) condensation products of 1 mole of phenol with about 5-30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-150 moles of ethylene oxide, (6) polyethoxylated quaternary ammonium salts having 2-50 moles of ethylene oxide combined with each mole of quaternary amine,

and (7) mixtures thereof, and the remainder water, for a period of time and at an elevated temperature sufiicient to produce a microfinished surface with controlled removal of metal from the foil surface.

14. The method of claim 13 in which the solution includes about 15% to 35% by weight of phosphoric acid.

15. The method of claim 13 in which the low-expansion alloy is about 29% nickel, 17% cobalt, 0.45% manga- 15 16 nese, 0.10% silicon, 0.02% carbon and the balance is 1 3,232,802 2/1966 Young et a1. 15618 iron. 3,436,283 4/ 1969 Chrisley 15614 16. The method of claim 13 in which the low-expansion 2,940,837 6/1960 Acker et a1. 156-18 alloy contains about 63.8% iron and 36% nickel. 3,120,458 2/1964 Evelbauer 156-18 XR 5 3,072,515 1/1963 Smolinski et a1 15620 References Cited 3,072,515 1/1963 Smolenski et al US L 3,125,475 3/1964 Livingston et al. 15620 mg UNITED STATES PATENT OFFICE 1 CERTIFICATE OF CORRECTION Patent No. 3, 530, 017 Dated September 22 1970 Inventor) Floyd L. Mickelson et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 5, line 34, change "15% and 35%" to -15% to 35%- C01 6, line 61, change "is being" to it being- Col 7, line 51 change "treated," to treated. C01 8 line 73, change "D to -O C01. 12 line 67, change "ExempIe" to -Examp eline 71, change "trlpoIyphosptate" to -tripolyphosphate-- Col. 15, line 7, delete "3,072 ,515 1/1963 Smolenski et a1."

SIGNED AN'L- QEALED (SEAL) Attest:

M. Fletcher, If. E. hr a LAttcafing off Y commissioner of Pam J 

